Answer:
Due to exothermic and endothermic reaction.
Step-by-step explanation:
The temperature of NaC2H3O2 solution rises because exothermic reaction takes place in the solution while on the other hand, the temperature of KCl solution fell because endothermic reaction takes place. In exothermic reaction, heat energy is released to the surrounding whereas in endothermic reaction, heat energy is absorbed from the surrounding so that's why the temperature of one solution increases while the other decreases.